User blog:Samuli.seppanen/Replacement parts
Three days at the forge/workshop allowed me to get lots of things done. Reinforced old little ladder beams I welded small wedge-shaped pieces to the tenons in the old little ladder beams: This should allow me to continue shooting with high-power without the need to (immediately) finish the new little ladder. Reinforced the curved field-frame bars Small pieces of steel were welded to the inside of the curves: The curves are now much stronger and can certainly handle the spring cords tuned to 350 hz. Forged parts for a new little ladder The main differences to the old ones are: * Beams are made from 5mm, not 4mm steel * The beam tenons are slightly narrower (9mm vs. 11mm) * The ends of the bars (tenons) have been forged flat, not folded * T-clamps were forged while hot into a simple form, not cold bent * The rivet for the crosspiece was forged from concrete reinforcing steel, primarily because I lacked rectangular pieces of steel Here are some pictures of the new little ladder beams: And of the hot-forged T-clamps (obviously unfinished) and crosspiece rivets: The wedge form of the tenons should be much stronger against twisting than the folded, flat tenon in the old beams. The slight increase in thickness of the beams should also help. The tenons were beated to the outside of the beams, so that after the notches are ground, very little, if any, bending is required to lock the tenons into field-frame bars. New bars for arms As I originally didn't see the need for the 14 dactyl cones, all my bars were a bit short. So I forged three new bars that are about 32cm long: These can be locked in place by bending their other end around the base of the cone. That should help prevent the cones from completely exploding near the hoop if they are overstressed. Although longer hooks increase the arm mass a bit, that new mass does not move much during a shot and thus does not affect performance much. New hoops for arms I was slowly running out of hoops for the arms, so I forged two new ones from fairly thick round steel: The thickness of the steel helps prevents spring cords from slipping over the hoops during pullback, and the extra weight doesn't really affect performance, because the hoops move a very short distance (=very slowly) during a shot. In other words, the residual energy in the arm after a shot is not much higher than with slightly thinner hoops. Modified locking pliers for stretching I briefly tested locking pliers for locking the spring cord while switching the winch to the other side of the stretcher. The problem with standard locking pliers are the teeth, which will rip the spring cord unless one releases the jaws really carefully while applying pressure to the winch on the other side. So I bought a pair of locking pliers and ground the teeth away. A little more fine-tuning is needed, but I hope that the grip will be good enough, plus that I can now simply winch the cord through the jaws without excessive chafing, like with my original wooden "clip". New forging techniques I tested a few new forging techniques. As mentioned, the little ladder beams were forged using a new and probably superior method. In addition I made one T-clamp by taking a flattish bar, splitting the end, bending it to a T-shape and then forging the part that fits against the little ladder beam flat. So there is no slit for the beam in this type of T-clamp. Given the dimensions in the text (1d wide, 3d high) I suspect this type is the correct one: 1d is a bit too little for a T-clamp with slit, because the slit "robs" about 0.25d of width. This new type of T-clamp would have to be riveted to the beam, though. The current slitted T-clamps have not so far required any rivets to stay in place. Category:Blog posts Category:Stretcher Category:Little ladder Category:Arms Category:Practical Category:Metalworking Category:Cheiroballistra Category:Backup